On a December day in 1848 the sailing ship Pekin
was becalmed off the Cape of Good Hope near Southern Africa
when a crew member spotted a strange creature in the water.
Careful examination of the animal by use of a telescope revealed
it to be snake-like, with a large head and shaggy mane.

Only two months before the HMS
Daedulus had reported seeing a sea serpent in that very
same region. Amid great excitement a small boat, it's crew prepared
to capture the animal, was lowered into the water. The captain,
Frederic Smith, watched from a distance, with concern for the
safety of his men, as the small boat approached the creature.
To the Captain's surprise the animal did not move at all as
the boat drew near. He was even more surprised when the crew
of the boat proceeded to tow the "creature" back to
the Pekin.

The sea serpent turned out to be a twenty foot
long piece of floating seaweed with a root shaped like a head
and neck. Could the Daedulus sea serpent been of similar origin?

Judging distance, size and motion of an object
in the sea is extremely difficult. Objects on land can be compared
to nearby trees and boulders. In the water only the waves offer
a clue to scale and the size of waves vary enormously depending
on weather conditions.

The movement of the waves can also suggest motion
where there is none. Arthur Adams, a ship's surgeon in the 1860's,
spotted what appeared to be a mysterious creature moving through
the water by using lateral undulations of it's body. His ship's
course was altered to intercept the animal and capture it. When
they approached the thing Adam's wrote:

"By this time, however, a closer and more
critical inspection had taken place, and the supposed sea monster
had turned himself into a long, dark root, gnarled and twisted,
of a tree, secured to the moorings of a fishing net, with a
strong tide passing it rapidly, and thus giving it an apparent
life-like movement and serpentine aspect."

The Daedulus affair might also be explained by
an abandoned native canoe painted like a snake. L. Sprague de
Camp suggested the owners of the canoe may have harpooned a
large sea animal, like a whale shark, and they were either spilled
into the sea when the animal surfaced under the boat, or jumped
in panic when they could not cut the line dragging the canoe.

One unusual, real creatures that might be mistaken
for a sea monster is the oarfish. The oarfish, Regalecus
glesne, is a strange eel-like animal that has been measured
at up to twenty-five feet in length. Some reports have described
specimens twice that size. The oarfish is bright silver in color
and has a high, bright red crest of spikes running down the
back of it's snake-like body. It's strange startling appearance
has led it to be identified as a monster on at least one occasion:
Two men were gathering seaweed on the coast of Bermuda in 1860
when they came across a serpent-like creature stranded in the
rocks. They killed it and they animal was reported as a sea
serpent until a naturalist eventually showed up and identified
the creature for what it really was.

An unusual species of frilled shark, Chlamydoselachus
anguineus, might also be taken for a sea serpent. Like the
oarfish it is eel-shaped. It has a single dorsal fin placed
well back along the body which can appear as a mane. The frilled
shark has an ancient history and is almost a living fossil.
It would truly be a likely candidate for a sea serpent if it
was only a little larger. So far the largest known frilled shark
was only six feet nose-to-tale. If there is a larger relative
of this animal swimming in the seas it might well be identified
as a sea serpent.

In 1880 Captain S. W. Hanna netted a long eel-like
shark that measured some twenty-five feet. While not matching
the description of Chlamydoselachus anguineus exactly,
it probably is a close relative and suggests there may be some
giant frilled sharks in the sea that could be taken for sea
serpents.

One dangerous candidate as a sea monster is the
salt water crocodile. These creatures, living in the India Ocean
and the area around south-east Asia and Australia have been
measured to lengths of 18 feet and weighing almost a ton. Unconfirmed
reports indicate they may get as long as thirty feet. They are
hungry, aggressive and often attack people.

The giant squid may account
for some sea serpent sightings too. Giant squids probably qualify
as sea monsters just as they are: Growing up to fifty feet long
with ten arms and eyes over a foot in diameter. If the cone
shaped squid head was sticking out of the water near close to
a visible arm the squid might look like a serpent head and tail
from a distance. (A famous serpent sighting off of Greenland,
by Hans Egede, in 1745 may be explained this way) Also a single
tentacle with a club of suckers on the end might look like the
head and neck of a Pleisosaur.

In 1875 the barque Pauline spotted a sperm
whale with a snake-like creature wrapped around it's mid-section.
The crew reported this sea serpent eventually dragged the whale
down to it's death. More likely the "snake" was the
arm of a large squid in battle with the whale.

Even mundane sea animals may be mistaken for
sea monsters. Fish or dolphins traveling together in a line
may appear as a series of undulating humps with dorsal fins.
Even a mass of low flying birds skimming across the water at
a distance have been mistaken for a single sea serpent.

The basking shark is one creature that is more
likely to be mistaken for a sea monster after it is dead, rather
than when it was alive. Basking sharks are the second largest
fish in the sea and grow to lengths of 40 feet. Like the great
blue whale they are harmless filter feeders with enormous mouths.
The shark skims the surface of ocean eating tiny floating plankton.
The water exits the shark's mouth through large gill slits on
the side of the head.

Because the gills of the basking shark rot quickly
after death the carcass can give the appearance of having a
long, narrow neck (like a pleisosaur)
without the head. Several basking shark remains have been misidentified
as sea monsters.

Some sea monster reports may not involve just
unusual creatures, but usual conditions. Right before a storm
at sea, air of two different temperatures can form layers just
above the surface of the sea. Perhaps seven or eight feet above
the waves. The different density of the two layers can cause
light to bounce forming a mirage. In
this case the mirage causes objects to be elongated, as if by
a fun house mirror, vertically, but not horizontally. Seals,
whales and dolphins breaking the surface under these conditions
will appear as thin, tall, unknown creatures.

Norse men often spotted these creatures and took
their appearance as an omen warning of an impending storm. Because
of the strange atmospheric conditions, rather than anything
supernatural, this warning was accurate.

A giant squid
could look like an extinct pleisosaur from a surface ship.